1. Field of the Invention
The present invention relates to an ignition advance angle controlling device for detecting knocking produced in an engine and for controlling the ignition advance angle to be a suitable value according to the amount of the knocking.
2. Description of the Prior Art
Fuel consumption and engine power output characteristics of an internal combustion engine are improved by advancing the ignition timing (the advance angle is increased) to an extent causing a suitable slight knocking state. However, since the optimum ignition advance angle varies according to the loading condition of the engine, a certain advance angle that may be optimum under a certain loading condition may be too large under another loading condition to cause much higher knocking. Such a much higher knocking affects the engine life. To solve the problem a device has been proposed to decrease the ignition advance angle at a time when a strong knocking state exceeding a predetermined level is detected.
FIG. 1 is a circuit diagram of one such known device including a knocking sensor 1 mounted on or adjacent an engine for detecting engine vibration which is substantially caused by knocking. Sensor 1 derives an electric signal having the waveform shown in FIG. 2, line (A). The signal derived from sensor 1 is applied to 2 is an amplifier or buffer 2, which drives averaging circuit 3 and peak detector 4 in parallel averaging circuit 3 derives a DC output signal having a mean or average value of a half wave rectified replica of the output signal of the sensor 1. Peak detecting circuit 4 detects peak values of the output signal of the knocking sensor 1 and holds the detected peak value. The held detected peak value is applied by circuit 4 to resistive voltage divider 5 having a tap for supplying one input signal to comparator 6, also responsive to the output signal of circuit 3. Comparator 6 compares the output signal of the averaging circuit 3 shown in FIG. 2(B) by waveform a and an output of the peak detecting circuit 4 shown in FIG. 2(B) by waveform b to derive a bilevel waveform (FIG. 2(C)). The positive portion of the waveform of FIG. 2(C) is derived in response to divided amount of the peak value exceeding the mean average value. An ignition advance angle controlling circuit 7 retards the ignition advance angle in response to the output of the comparator 6. Reset circuit 8 resets the peak value detected by circuit 4 each time there is an ignition or at a predetermined time interval.
If knocking occurs in an engine controlled by the prior art circuit having substantially the aforementioned basic construction, peak detecting circuit 4 derives a relatively high amplitude output signal, which is much larger than the mean value of the output of the knocking sensor 1 derived when knock does not occur; the divided signal value derived from divider 5 may also exceed the mean value. Accordingly, each time a knock occurs, an output signal is derived from the comparator 6 and the ignition advance angle is retarded by a certain small amount to prevent occurrence of a very strong knock.
In the known device, the ignition advance angle is immediately reduced by a predetermined amount when a knock exceeding a certain amount is detected. The advance angle is reduced by the same amount even if there is a difference in the knock level. Therefore the advance angle is excessively decreased for slight knocks but may be insufficient for strong knocks and be unable to prevent the strong knocks. If the ignition advance angle is excessively decreased, the fuel consumption and the output power characteristics are still inferior. In accordance with this invention, these problems are substantially rectified.